This invention relates to fluidized bed reactor systems used for the combustion of crushed coal in industrial or utility type applcations. Presently used fluidized bed systems transport crushed coal and limestone to the boiler with transport air in a condition known as dilute phase pneumatic transport. The transport air upon entering the bed has been shown to form a significant void extending from the feed point upward into the bed. This void region is characterized by severe channeling and spounting of solids inasmuch as when crushed coal enters the bed, volatiles and feed fines become entrained in the spout, then elutriated and exhausted from the system. This situation contributes to lower combustion efficiency since the fines are not able to burn out in the bed but are rapidly extinguished after they become elutriated. However, combustion of volatiles is promoted above the bed so as to make it difficult to maintain desired bed temperatures.
A partial solution to the problems that accompany fluidized bed combustion is overcome by feeding crushed coal only in an overbed arrangement. Here the transport air is released above the bed whereby it will not affect the bed dynamics. However, this arrangement is not efficient since the feed coal must be double screened to first remove the fines, for if the fines fall freely upon the top of the bed they are rapidly elutriated and not used for combustion in the bed.